f(x) (Korean: 에프엑스; pronounced /ˌɛf ˈɛks/) is a five member South Korean girl group formed by SM Entertainment in 2009. The name is a play on the mathematical notation for function, with "f" signifying "flower" and "x" representing the female's double X chromosome. The group members have also been nicknamed "function girls". The group made their debut on September 1, 2009 with release of a digital single "La Cha Ta" (stylized as "LA chA TA"). The quintet consists of Victoria, Amber, Luna, Sulli and Krystal.Krystal Jung was first spotted by SM Entertainment in 2000, which earned her a small role in a short segment of Shinhwa's "Wedding March" music video. Sulli Choi first debuted as a child actress in 2005 when she was selected to play young Princess Sun-hwa in the SBS television drama, The Ballad of Seo-dong. In 2006, SM Entertainment recruited Luna after seeing her performing on SBS's television program, "Truth Game". Victoria was scouted by SM in Beijing in September of 2007 at a dance competition. 2 months later, Amber was cast from an audition in Los Angeles, California, where she was one of two people (one male) selected to be trainees. SM first released a teaser preview of the group via YouTube on August 24, introducing them as "Asia's Pop Dance Group." For five days, SM individually released information through news portals and posted pictures of each member on SM Town's official website, starting with Korean member Sulli on August 26, Taiwanese-American member Amber on August 27, Korean-American member Krystal on August 28, Korean member Luna on August 29, and lastly the Chinese member Victoria on August 30. On September 1, the group's first single "La Cha Ta" (stylized as "LA chA TA") was digitally released.
Following their first performance at the Samseong-dong Fashion Center on September 2, the music video was screened and released online the next day. The group's first broadcast performance of "La Cha Ta" was held at MBC's music show Show! Music Core on September 5. On October 7, the group also released the electro-pop version of the digital single, "Chocolate Love", alongside their label mate Girls' Generation. The single was released for the promotion of the 4th edition Blacklabel series of LG CYON phone, LG Chocolate (BL40. It was announced by SM Entertainment that Amber returned from USA after a long leave since June 2010 and that f(x) are planning to release a studio album in the first half of the year. The first teaser photo for their full-length album entitled Pinocchio was released on April 7, 2011 at the f(x) official website. The MV teaser for the lead single, "Pinocchio (Danger)", was released on April 15, 2011. The album was released on April 20, 2011 and the group held their first comeback stage through KBS’s Music Bank on April 22, 2011. The group have achieved 8-wins from the music shows, namely M! Countdown, Music Bank and Inkigayo. On June 8th, it was announced that f(x) will be releasing their repackaged album of Pinocchio, titled "Hot Summer", on the 14th. It will include all 10 songs from their first album and new track "Hot Summer" (written by Thomas Troelsen and Remee), their OST song for "Paradise Ranch" and digital singles "Chu" and "La Cha Ta."f(x) "Hot Summer" Song
f(x) with their red costume in their video clip in "Hot Summer"
f(x) choreography concept in their video clip
f(x) and their cool costume concept
f(x) cool pose